Computer Science – Performance
Scientific paper
Aug 2003
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003basbr..23...49a&link_type=abstract
Boletim da Sociedade Astronômica Brasileira (ISSN 0101-3440), vol.23, no.1, p. 49-50
Computer Science
Performance
Scientific paper
Precise positions of ICRF extragalactic radio sources derived in the Hipparcos Celestial Reference System (HCRS) allow one to access the relative orientation between the HCRS and the ICRF. In this context, a long term observational program is being carried out at three distinct instruments: the Valinhos CCD Meridian Circle, the 0.6m and the 1.6m Cassegrain telescopes at Laboratório Nacional de Astrofísica, Brazil (LNA). The list consists of 409 ICRF radio sources distributed between +20o < d < -80o in the sky. Here, we present pilot, comprehensive results for a set of sources representative of the whole program. Reduction of the 0.6m CCD frames (10'x 10', 1 pixel = 0".6) are referred to the UCAC catalog and to Tycho2-based star positions derived from the Valinhos Meridian Circle. Reduction of the 1.6m CCD frames (5'x 5', 1 pixel = 0".3) are referred to the positions of intermediary brightness, secondary stars derived from the 0.6m reductions. These CCD frame reductions furnish optical ICRF source positions. An investigation of the astrometric performance of all these instruments and the UCAC catalog in the scope of obtaining precise positions for the optical counterparts of the ICRF sources was carried out. The average optical minus radio position offsets for the 0.6m telescope were +4mas +/-8mas(41mas) and +4mas +/-8mas(42mas) for R.A. and Dec. respectively, using the UCAC in the reductions. Using the Valinhos positions, the offsets were +90mas +/-30mas (71mas) and -31mas +/-29mas (72mas). The errors of the mean values (plus/minus) and the standard deviations about the mean (parenthesis) are given. For the 1.6m, the results regarding the UCAC were -11mas +/-9mas(45mas) and +7mas +/-9mas(46mas) in the same sense as before. Plots against R.A., Dec., magnitude (V and R) and color (V-R) show no dependences. We conclude that the astrometric performance of the 0.6m telescope rivals that of the 1.6m for the bright objects, and that the UCAC furnishes the best representation of the HCRF for our set of CCD observations.
Andrei Alexander H.
Assafin Marcelo
da Silva Neto Dario N.
Monken P. T.
Vieira Martins Roberto
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